DYNAMICS. 35 



changed by the action of those bodies on one ano- 

 ther. 



This follows from 71. 



74. If A and B be the masses of two bodies 

 that move in the same straight line toward the 

 same parts with the velocities a and b ; and if A 

 and B are hard or soft bodies, so that after colli- 

 sion they go on together, with the velocity v, 



If b is negative, so that the bodies meet one another, 



the velocity after collision, or v = " } ; and 



A. -f- A5 



if A a = B 6, the velocity after collision is nothing, 

 as before demonstrated. 



When the bodies are equal, these two formulas be- 



a -j- b , a b 

 come ' and -- . 

 2 2 



If B is at rest, or b 0, the formula is v = -- ~ . 



.A. -p jj 



If B is an immoveable obstacle, it may be considered 

 as a body that is infinite in respect of A, so that 

 the denominator A -j- B is infinite, and therefore 



c 2 75. If 



